Study on the lap-splice behavior of post-yield deformed steel bars in ultra high performance concrete

Abstract

Ultra high performance concrete (UHPC) is a type of cement-based composite material with ultra-high strength, high toughness and excellent durability. Furthermore, it has ultra-high bond strength of steel bar in UHPC. Influences of splice length, fibre volume fraction, stirrup ratio and steel bar yielding on the splice strength were studied by 21 groups direct tensile lap-splice tests. Two failure modes, splitting pull-out failure and steel bar rupture failure, appeared in the test. The splice strength depends on the splitting strength of UHPC. The steel bar rupture failure occurred under rather small embedment length. Based on the elastic model of partly cracked thick-walled cylinder, in the post-yield phase, the localized splice strength in elastic and plastic domains were calculated considering and ignoring the friction between the bar and UHPC, respectively. The stirrups are equivalent to the thickness of UHPC cover according to ACI 318–19. The mean splice strength was calculated by averaging the bond strengths of elastic and plastic domains and agrees well with the test results. The results calculated with the formulas of GB50010-2010, ACI 318–19 and ACI 408R-03 may be conservative to estimate the minimum yield splice length (MYSL) and minimum ultimate splice length (MUSL). The proposed theoretical method in this paper can calculate the MYSL and MUSL accurately. The MUSL is about 1.8 times of MYSL.